An internal combustion engine, wherein an elevated expansion ratio is provided by utilization of a holding tank, is described in U.S. Pat. No. 6,907,859 of B. J. Robinson (Robinson), the inventor of the present invention. For appreciation of the present invention, it is useful to review the operations of the four-stroke form of the gasoline engine and the diesel engine, and particularly the description of the Robinson engine. Information on the construction of the engine, disclosed in the Robinson patent, is incorporated herein by reference.
In the four-stroke form of the gasoline engine, the movement of a piston in its cylinder is characterized by four strokes of the piston, in conjunction with operation of an intake valve and an exhaust valve generally located in the cylinder head. The four strokes occur in a repeating sequence, the sequence of the four strokes being: an induction stroke, a compression stroke, a power (or expansion) stroke, and an exhaust stroke. During the induction stroke, the piston moves away from the head of the cylinder to produce a vacuum that draws in a mixture of air and fuel vapors via the intake valve. During the compression stroke, the intake and the exhaust valves are closed, and the piston moves towards the cylinder head to compress the air-fuel mixture. Approximately at the beginning of the power stroke, there is ignition of the air-fuel mixture and, during the power stroke, the expanding gases produced by the combustion of the fuel drive the piston away from the cylinder head. During the exhaust stroke, the piston moves towards the cylinder head to drive the exhaust gases out of the cylinder via the exhaust valve. In the usual construction of such an engine, an intake manifold is provided for bringing air and fuel from a carburetor or fuel-injection assembly to the intake ports of the cylinders, and an exhaust manifold is provided for removal of combustion gases via exhaust ports of the cylinders.
It is useful to compare operation of the gasoline engine with the diesel engine. In the case of the gasoline engine, both fuel and air are present in the cylinder during the compression stroke. The temperature produced in the gases within the cylinder is below the ignition temperature of the air-fuel mixture so as to avoid premature ignition of the air-fuel mixture. Ignition is produced by an electric spark of a spark plug, mounted within the cylinder head. In a modern engine, activation of the spark plug at an optimum moment, relative to the time of occurrence of the power stroke, is provided by a computer. In the case of the diesel engine, only the air is present in the cylinder during the compression stroke. The geometry of the piston within the cylinder of the diesel engine differs somewhat from the corresponding geometry of the gasoline engine such that the compression stroke of the diesel engine provides significantly more compression of the gases within the cylinder (a compression ratio of approximately 15:1) than occurs in the gasoline engine (a compression ratio of approximately 8:1). As a result, in the diesel engine, the temperature of the air is raised by the compression stroke to a temperature high enough to ignite fuel. Accordingly, in the diesel engine, the fuel is injected into the cylinder at approximately the beginning of the power stroke, and is ignited by the high air temperature.
It is observed furthermore, that in the usual construction of a gasoline engine and of a diesel engine, the ratio of the expansion of the volume of cylinder gases, final volume divided by initial volume of the power stroke, is equal to the ratio of the compression of the volume of the cylinder gases, initial volume divided by final volume of the compression stroke, for engines without the feature of elevated expansion ratio provided in the Robinson patent. The expansion of the cylinder gases in the power stroke is accompanied by a reduction in the temperature of the cylinder gases. Well-known theoretical considerations show that an important consideration in determining the efficiency of the engine is the ratio of the gas temperature at the beginning of the power stroke to the gas temperature at the end of the power stroke. A greater temperature ratio is obtained in the case of the diesel engine than for the gasoline engine. This is one of the reasons that the diesel engine can operate more efficiently than the gasoline engine.
The engine of the Robinson patent includes, for each cylinder, an intake valve and an outlet valve, and furthermore includes a return valve and a discharge valve. The return valve closes and opens a passage between the internal space of a cylinder and its holding tank, and the discharge valve closes and opens a passage between the holding tank and a return manifold. In Robinson, the holding tank is formed within an arm of the return manifold, the return valve is located in a return port of the cylinder head at an outboard end of the manifold arm, and the discharge valve is located at the inboard end of the manifold arm adjacent to a central chamber of the return manifold. The function of the holding tank, in conjunction with the additional valves and the return manifold, is to give the engine an elevated expansion ratio while simultaneously being able to reduce the compression ratio for additional fuel savings. In the operation of the Robinson engine, gasses extracted from respective ones of the cylinders during a portion of the compression stroke (an air-fuel mixture in the case of a gasoline engine, and air in the case of a diesel engine) are recirculated via the respective holding tanks and the return manifold to be reinserted into the cylinders of the engine.
Other examples of engines employing additional manifolds and valves are presented in Date, U.S. Pat. No. 3,878,826, and Amano, U.S. Pat. No. 4,192,265.